Wind turbines have begun to be sited at offshore locations. The use of wind turbines to generate electricity offshore presents some unique challenges that are not encountered onshore. This includes, among other things, the provision of a seaworthy foundation or platform for the turbine, and the construction of the wind turbine tower and placement of the wind turbine aloft on the tower as well as the transmission of energy generated to shore. In prior art offshore wind turbines, a solid foundation is poured with pilings into the sea floor and the tower is erected on this foundation with the use of large and complicated sea cranes which also are used to put the nacelle and rotor aloft on the tower. Offshore turbines installed in this manner must be placed in relatively shallow water so that the foundation is not excessively tall and expensive and they can only be erected when weather conditions are suitable for operating the sea crane. It would be desirable to provide a method of installing offshore wind turbines in deep waters which would allow the wind turbine to be assembled in an area near shore where it is protected from severe weather.
Conventional offshore wind turbine foundations and pilings are a significant impact to the sea floor ecology and at the end of the turbine's life the foundation may present a navigation hazard. It would be desirable to provide a way of deploying offshore wind turbines that have a lower impact on sea floor ecology and do not present a navigation hazard after the turbine is decommissioned.
Prior art offshore wind farms most commonly collect the output from each of the wind turbines and step the voltage up to high voltage for transmission to shore via an electric cable. The cost of this transmission system can be prohibitively large especially if the wind farm is very far from shore. It would be advantageous to provide an alternate method for transmitting the energy produced by the wind turbines. The placement of these prior art turbines offshore, but near land, has caused controversy because the turbines are easily visible from populated areas. By placing the turbines far offshore the visual impact is lessened and the permitting will be easier. This is because the offshore structure becomes much less visible if it is placed at least 12 miles from shore.
There has been some research into using excess wind power or remote wind power to produce hydrogen which could be used in a fuel cell to provide peaking power. Since there is not much infrastructure for transmission and use of hydrogen, any hydrogen produced must be used at the site or packaged for safe transportation. Furthermore, new infrastructure must be adopted by society at large before there will be a significant market for hydrogen. It would be desirable to provide a method for allowing the products of excess wind energy or remote wind energy to be used directly in the existing chemical fuel infrastructure.
There is currently a growing market for “green power” sold at a premium price by some utilities and “green tags” which represent the environmental attributes of green power and are available for purchase where the local utility does not have a “green power” pricing program. This demonstrates that many consumers want to purchase electricity which has been produced in an environmentally friendly way, and that they are willing to pay a premium price for this product. The market for chemical fuels (gasoline, natural gas, etc) currently has no equivalent, with the possible exception of biodiesel fuel. It would be desirable to provide environmentally friendly chemical fuels to the marketplace where they could be marketed at a premium price to environmentally conscious consumers.
In prior art groupings of wind turbines, usually in the form of an onshore wind farm, grid quality AC power is produced in the nacelle of each wind turbine, in phase with each other, and all the power is summed through a common transformer of substation and delivered to the utility grid. Although effective, this requires that each of the turbines have all equipment necessary to produce grid quality AC power including gearbox and generator, and possibly a power converter. Often this equipment is heavy and located in a nacelle at the top of a tower which raises the center of gravity of the whole tower, turbine, and foundation system increasing the demands on the tower and foundation. It would be desirable to provide a method of summing power such that more equipment could be located at the base of a tower and such that many turbine rotors could share one set of equipment.